1. Field of the Invention
The present invention relates to an electric fuel pump which is mounted in a fuel tank of an automobile or the like, and which forcedly delivers fuel to an engine, and particularly to an electric fuel pump in which the noise level can be lowered and the efficiency can be improved.
2. Description of the Related Art
FIGS. 6 and 7 are an enlarged partial perspective view of an impeller of an electric fuel pump of the conventional art which is disclosed in, for example, JP-B-63-63756, and an enlarged perspective view of the periphery of a radial seal portion of a pump base of the pump.
In the figures, 10 denotes the impeller which has many vane pieces 21 in an outer peripheral edge portion of a disk-like shape. The vane pieces 21 are divided into front and rear groups by a partition wall 22, and a vane groove 23 is formed between the vane pieces 21. The reference numeral 9 denotes the pump base which constitutes a pump casing (not shown), and which has an arcuate strip-like pump passage 13, a suction port 14, a discharge port 15, the radial seal portion 9a for preventing a reverse flow of fuel from occurring, and an end face 9b which changes the flow direction of the fuel.
When the impeller 10 is rotated in the pump casing (not shown), the fuel sucked from the suction port 14 flows into the vane grooves 23, is provided with a kinetic energy by the vane pieces 21, and then forcedly sent through the pump passage 13 toward the discharge port 15. The fuel which is forcedly sent to the discharge port 15 as described above collides against the end face 9b of the radial seal portion 9a which is formed in the final end of the pump passage, and is then discharged from the discharge port 15 while the direction is changed.
In this configuration, therefore, the fuel portions respectively entering the right and left vane grooves 23 which are divided into front and rear groups by the partition wall 22 simultaneously collide against the end faces 9b of the radial seal portions 9a. Consequently, the configuration has a problem in that the level of noises due to the fuel collision is high.
As a countermeasure against this problem, for example, known is the configuration which is disclosed in JP-A-60-173390 and shown in FIG. 8. In an impeller 10 of the configuration, vane pieces 21 on both the sides of a partition wall 22 are shifted from each other by 1/2 pitch, so that timings when the fuel portions respectively entering vane grooves 23 on both the sides of the partition wall 22 collide against end faces 9b of radial seal portions 9a are shifted from each other. As a result, the impact force due to the fuel collision is reduced, thereby lowering the noise level. The periphery of the radial seal portion is configured in the same manner as above-described FIG. 7.
In the configuration which is disclosed in JP-A-61-59283 and shown in FIGS. 9 and 10, a step 9c is disposed in an end face 9b of each radial seal portion 9a of a pump base 9 which constitutes a pump casing (not shown), whereby timings of fluid collision are shifted from each other to lower the noise level. Furthermore, the outer peripheral face of each vane piece 21 is protruded from that of a partition wall 22 in an outer peripheral direction, so that a reverse-flow region (a region where the pumping function is impeded) is prevented from being produced immediately above the partition wall 22, whereby the pump efficiency is improved.
Recently, needs for lowering the operating sound level and reducing fuel consumption are increasing. In order to satisfy the needs, in an electric fuel pump of the conventional art, a countermeasure in which the shape of an impeller is changed so as to lower the operating sound level as described above, or that in which the shape of an impeller is changed and the shape of a pump base is changed so as to lower the operating sound level and improve the pump efficiency is taken. From the viewpoints of dimensional accuracy and mechanical strength, however, a pump base is usually produced by aluminum die casting. Consequently, there is a problem in that modification or production of production dies is very expensive.